So reporting back -- it could not have gone better. Yes it would be better to have a couple of day -- to be able to go up to the glacier, to walk down from the midpoint on the Agulle du Midi trip etc. BUT it went perfectly and since it might be our only chance we took it. My husband is visually impaired and that is likely to get much worse ere long so we are doing things now while we can.
Booked BlaBlaBus -- which I had my doubts about, but it was a comfortable ride both ways. And the driver took us through a car wash on the way down. Only issue was that the return bus was not painted BlaBla colors nor did it have so much as a handwritten placard in the front window to indicate it was bus # whatever BlaBlaCar. We came close to missing the ride home. because it wasn't a BlaBla and there were many other buses. We asked the driver and so made the bus.
Took 9:30 bus from Annecy, got there about 11:10 and the Aquille du Midi station is nearby. Not crowded, no significant lines -- our 'car' to the top was combined with another since there were so few reservations -- There were probably 25 of 30 with the combined cabins.
Clear gorgeous day; it was not even that cold on top and so our not very warm improvised outfits were fine. Just so beautiful. WE climbed to many but not all the viewpoints, went out in the clear box which involved a wait of maybe 5 minutes -- the person managing it takes your picture with your camera or phone since they don't allow backpacks or photo gear in the box. Everyone wears big felt slippers over their shoes to protect the transparent floor.
After a goodly time drinking in the stunning clear view -- watching hikers and skiers etc and wishing we were among the few taking the further gondolas on to Italy -- if we every come back, we are definitely doing that -- we headed back down to the first level where there is a bar, picnic tables etc. Got hot sausage sandwiches and drinks and enjoyed just sitting there in that beautiful place -- caught the 2:15 gondola back down and hung around a cafe until bus time.
Could not have gone better -- no real crowds, no rush and stunning weather --